1. Field of the Invention
The present invention relates to an automatic focus detecting and adjusting apparatus for optical instruments. More precisely, it relates to an automatic focusing apparatus which detects a moving object, that is to be photographed, by following the movement of the object and automatically end precisely focuses on the object.
Also, the present invention relates to an automatic focusing apparatus in which a backlash of a lens driving system can be controlled.
2. Description of Related Art
In a known focus detecting apparatus (automatic focusing apparatus) of a camera having a moving object predicting AF mode, a projected position of the moving object (i.e., a future position of the object after a predetermined period of time) is determined in accordance with the movement of the object, so that the focus is adjusted for the projected position. In such a known focus detecting apparatus having a moving object predicting AF mode, the mode is switched between the moving object predicting AF mode and a normal AF mode in which the focus is adjusted for a moving or stationary object at the moment of measurement of the object distance, respectively. Consequently, for example, in sports photographing, since an object to be photographed, i.e., a player, is neither constantly at rest or in movement, it is necessary to frequently switch the AF mode in accordance with the state of the player.
However, frequent switching of the AF mode is troublesome. Furthermore, if sudden movement of the object occurs when a picture is taken in the normal AF mode, a photographer is unable to quickly switch the AF mode to the moving object predicting AF mode, or vice versa, resulting in a missed photograph.
Furthermore, in a conventional moving object predicting AF mode, when the object is moving, the projected position thereof at which the object would be in a predetermined period of time is predicted, so that the focus is adjusted for the projected position, as mentioned above. The focusing lens is moved by a predetermined displacement in accordance with the predicted position preceding or subsequent to the completion of movement of the object.
The prediction requires a complex calculation which takes a relatively long time, resulting in decreased follow-up efficiency. To increase the calculation speed, it is necessary to use an expensive CPU (central processing unit).
There is a known optical instrument, such as a camera, having an automatic focusing function in which an object distance or amount of defocus by a taking lens is photoelectrically detected to automatically indicate "out of focus" or "in focus" (focus indication) or automatically move the taking lens to a focal position (automatic focusing). In a focus detecting apparatus incorporated in such an optical instrument, continuous measurements of the object distance are sometimes carried out to increase focusing accuracy.
However, particularly in a phase difference detecting type of focus detecting apparatus, a measurement error exists for the same object under the same measuring conditions when the contrast of the object is low. Consequently, due to the measurement error, the focusing lens unit which is located at a correct focusing position is moved to an incorrect position (i.e., out of focus position) by mistake, or a symbol representing "in focus" blinks to indicate "out of focus".
Furthermore, an automatic focusing apparatus, in which the object distance or the defocus amount of the object image is photoelectrically detected so that the focusing lens unit is moved in accordance with the detected result to effect automatic focusing, is also known.
In the above described automatic focusing apparatus, backlash between an AF motor (drive source) and focusing lens unit driving mechanism occurs. Therefore, if the direction of movement of the focusing lens unit changes, it is necessary to eliminate the backlash effect. To this end, in the prior art, a value (displacement value) corresponding to the backlash is added to a value (displacement value) calculated in accordance with the defocus amount, so that the focusing lens unit is moved by the resultant displacement.
The primary object of the present invention is to provide a focus detecting apparatus which can check whether an object to be photographed is a moving object.
Another object of the present invention is to provide an automatic focus adjusting apparatus in which when the object is a moving object, a focusing lens is moved in accordance with the speed of the moving object.
Still another object of the present invention is to provide a focus detecting apparatus free from maloperation caused by measurement error, particularly at low contrast.
Still another object of the present invention is to provide an automatic focusing apparatus in which the displacement of a focusing lens unit necessary to absorb a backlash can be easily calculated to effect precise control.